In a multiple zone intrusion alarm system for protection of a plurality of zones within a building or other installation, a central control unit is coupled via an interconnecting cable to a plurality of transceivers or other sensors each disposed at a respective area being protected. Each transceiver typically includes a transmitting transducer for establishing an energy pattern in the associated protected zone, a receiving transducer for receiving energy returned from the protected zone and from objects therein and a receiving preamplifier for augmenting the received signal amplitude for conveyance on the interconnecting cable back to the central control unit. Signal processing circuitry is included within the central control unit and is operative in response to signals from the transceivers to discriminate valid intruder signals from noise and spurious signal conditions and to provide an output indication of intruder presence.
In order to test the performance of the alarm system in a particular zone, the entire installation must be secured to assure that all of the zones of the system are known to be free of possible intruders in order for a valid test to be conducted in each of the zones. It has been customary in performing a test of a multiple zone alarm system to clear the entire installation so that respective zones can be tested. Alternatively, the transceivers in the zones other than the one to be tested can be capped to prevent transmission or reception of energy within the associated zones, and thereby render these zones inactive. However, individuals who may be present during the transceiver capping procedure are thereby instructed how to defeat the alarm system or how to disable the transceiver. In addition, failure to remove a cap after a test will result in the associated zone remaining inoperative with possible serious consequences by reason of failure of the system to detect an intruder in the inoperative zone. Clearing of the entire installation for conduct of a test suffers the disadvantages of time and personel required to maintain the installation in a secured condition during conduct of the test.